When Luther returns tonight on BBC America (10/9c), the show’s titular antihero will be sporting a fancy new accessory — a smile.

Yep, John Luther actually experiences moments of pure happiness over the course of Season 3’s four-episode, four-night rollout, and that’s due in no small part to the arrival of Sienna Guillory (Resident Evil) as the intense super-sleuth’s new love interest, Mary Day.